Condition responsive process timer



July 23, 1968 R. s. LUNDIN CONDITION RESPONSIVE PROCESS TIMER mvENToRRober .S lan du:

Filed Aug. 13. 1965 uk (w United States Patent O 3,393,604 CONDITIONRESPONSIVE PROCESS TIMER Robert S. Lundin, Thomaston, Conn., assignor toGeneral Time Corporation, New York, N.Y., a Corporation of DelawareFiled Aug. 13, 1965, Ser. No. 479,553 18 Claims. (Cl. 88-24) ABS'I'RACTOF THE DISCLOSURE A photoprocess Controller having an RC interval timerwhich utilizes a photosensitive resistor, in the capacitor`s chargingpath, which is optically coupled to a lamp. An adjustable, transistor,Constant current `source in the charging path maintains the chargingcurrent Constant. The photosensitive resistor |and constant currentsource respectively compensate for lamp deterioration and line voltagefluctuations thereby maintaining Constant the lumen-second light outputof the lamp, which output is adjustable 'by varying the level ofcharging current. The charging current circuit is one side of a bridgeCircuit, whose other side inclu-des a Zener |diode which provides fixedvoltage source. A detector, connected across the bridge sides, isenergized when the voltage across the charging capacitor -reaches thefixed voltage of the Zener to operate a latching circuit which turns offthe lamp to end the timing cycle.

The present invention relates generally to a condition responsiveprocess timer. More specifically, it |relat'es to a conditionzresponsive timer particularly 'adapted for use as an input controller.The disclosed embodiment of my invention is directed to a lumen-secondController operating to control a light source such that its lightoutput, in lumen-seconds, is held to an adjustably preset value.

In the p'hotocopy and photoprocessing industries there has been a greatneed for a lumen-second Controller that compensates for line voltagefluctuations and lamp deterioration. It will be appreciated that eitherone of these factors produces variations in the quantity of lightemitted by a lamp. Exposure time must therefore 'be varied in order toproperly expose photosensitive papers. Failure to compensate for thesetwo factors gives rise not only to poor quality, but to nonuniformitiesin exposure.

Similar problems exist in -all processing industries Where it is desiredto supply a given quantity of energy. The Circuit described herein usesa light responsive element and is specifically applica-ble tophotography. T'hose skilled in the processing -arts will app'reciatethat the circuit of the invention may be applied to many other processesby substituting for the light responsive element an element responsiveto the form of energy to be supplied.

Accordingly, it is an object of my invention to provide an intervaltimer.

A further object of the invention is to provide an interval timer of theabove character adapted for operation as an input controller.

A further object is to provide a condition responsive timer of the-above Character for controlling condition producing means.

A still further object is to provide a timer lof the above Characterwhich responds to the existing level of a condition and modifies itscontrol of the condition producing means accordingly.

A yet further object of the invention is to provide an electronic timerof the above character which compensates for fluctuations in linevoltage.

An additional object is to provide a timer of the above character whichcompensates for variations in the con- ICC dition level produced by thecondition producing means.

Another object of the present invention is to provide a controller ofthe above character adapted for use as a lumen-second Controller.

Still another object of the present invention is to provide alumen-second controller of the above character which `may be -adjustablypreset so -as to provide a predetermined lumen-second light output.

Other objects of the invention will in part be obvious and will in partappear h-ereinafter.

The invention accordingly comprises the features of construction,combination of elements, and arrangement of parts which will beexemplified in the construction -hereinafter set forth, and the scope ofthe invention will be indicated in the claims.

For a fuller understanding of the nature and objects of the invention,reference should be had to the following detailed |description taken inconnection with the accompanying drawing, in which the sole figure is adetailed circuit schematic diagram, partially in block form, of apreferred embodiment of my invention adapted as a lumen-secondController.

Broadly stated, my invention is directed to an interval time-r of thetype described in the copending application of Klaus Wallentowitz, Ser.No. 405,503, filed Oct. 21, 1964, for Electronic Timer Circuit. Thiscopending application is ass-igned .to the same assignee as the presentapplication. Accordingly, in my invention there is provided a bridgecircuit consisting of first and second sides connected across apotential source. The bridge sides are connected to a detector circuitwhich controls the condition of a latch circuit. The latch circuit inturn controls the energization of an output relay having operativelyassociated relay contacts connecting condition producing means to asource of electrical energy.

One side of t-he 'bridge includes a timing capacitor and an impedanceelement through which charging current fiows to the timing capacitorfrom the potential source. Unlike the timer disclosed in the above-notedcopending application, in my invention, this impedance element is acondition responsive device whose imped-ance value is proportional tothe existing level of a Condition produced by the condition producingmeans. The timing capacitor charges at a rate which is a function of themeasured Condition. When the potential across' the timing capacitorreaches a predetermined voltage relative to a fixed reference potentialestablished at the other bridge side, the detector, connected across thetwo bridge sides, is energized to condition the latch and therebycontrol the energzation condition of the output relay.

The disclosed embodiment of my invention -is specifi- Cally directed .toa timer for use as a lumen-second controller and thus the conditionproducing means takes the form of a lamp. The condition responsivedevice is a photosensitive 'resistor optically coupled to the lamp. Inaddition to the photosensitive resistor and in further distinction fromthe timer of the aforesaid copending application, a variable conductancedevice is included in the charging path for the timing capacitor so -asto regulate the charging current according to the setting of apotentiorneter which, in and of itself, determines the light output, 'inlumen-seconds, of the lamp. The controller responds to the existinglight output to automatically control the duration of the interval ofthe lamp's illu'mination so as to hold the lumen-second light output ofthe l-amp at a set point value established by the setting of thepotentiometer.

The timer of my invention is further rendered insensitive to powersupply variations. This is achieved in a novel manner by supplying afixed reference potential to the detector. The potentiometer isenergized from a second fixed potential such that for a particularsetting, a constant fract-ion of this second fixed potential is`supplied to a` control terminal of the variable conductance deviceconnected in the charging path for the timing capacitor. Thus, thecharging current supplied to the timing capacitor is maintained constantfor a particular set point rega-rdless of va'riations in the powersupply for the interval timer. Thus the rate at which the timingcapacitor charges to the voltage of the fixed reference potentialsupplied to the 'detector is unafected by power supply va'ri-ations.

Moreover, since the interval times of my invention monitors only thelight output of the lamp, the precise lumen-second output is obtainedregardless of variations in the lamp power supply and regardless of lampdeterioration.

Referring now to the sole figure of the drawing, the conditionresponsive process timer, constructed according to my invention andgenerally indicated at 10, operates as an interval timer timing theinterval during which a lamp 12 is energized. According to the dsclosedapplication of the timer 10, the lamp 12 is utilized in a photocopyingprocess wherein it gives off light for developing photosensitive paper.The particular manner in which the photocopying process is carried outand the specific optical system employed is not material to theinvention embodied in the timer 10. The function performed by the timer10 is to accurately control the lumen-second light output of the lamp 12so as to properly expose the photo- Sensitive paper on which the copiedsubject matter is developed.

The timer 10 includes a bridge side 14 and a bridge side 16 whichcooperate with a detector circuit 18, a latch circuit 20, and an outputcircuit 22 in order to control the energization of an output relay K1.Output relay K1 includes operatively associated relay contacts Kla forcon- -trolling the energization of the lamp 12.

Referring more specifically to the drawing, a source of positivepotential is connected to an input terminal 24 while a source ofnegative potential is connected to input terminal 26. Terminal 24 isconnected through a switch S1 to a positive buss 28. One side of thelamp 12 is connecta'ble to buss 28 through the relay contacts Kla ofoutput relay K1 while the other side of the lamp is connected to agrounded 'buss 30. It is to be understood that, although the timer 10and lamp 12 are shown as sharing a common power supply, in practice theymay be energized from separate power Supplies.

Bridge side 14 comprises the series circuit including a diode D1, aresistor R1, the emitter-collector circuit of a transistor Q1, a timingcapacitor C1, a diode D2 and a diode D3 connected between busses 28, 30.According to the dsclosed embodimen-t of my invention as directed tocontrolling the lumen-second light output of lamp 12, resistor R1 is aphotosensitive resistor which is positioned so as to be opticallycoupled with the lamp 12. A Zener diode D4 and a resistor R2 areconnected in series across the busses 28, 30. A potentiometer P1 isconnected across the Zener diode D4. The base of transistor Q1 isconnected to the adjustable tap 31 of the potentiometer P1 so as to tapoif a predetermined fraction of the fixed potential developed acrossZener diode D4. Input terminal 26 is connected by a lead 32 and aresistor R3 to the junction between the diode D1 and the photoresistorR1. The negative potential applied to terminal 26 serves to maintain aforward voltage drop across diode D1 which, as will be seen, compensatesfor the base-emitter junction potential of transistor Q1.

Bridge side 16 is comprised of the series circuit of resistor R andZener diode D5 connected 'between the busses 28, 30. The emitter of atransistor Q2, included in the detector circuit 18, is connected to ajunction 34 between the resistor R5 and Zener diode D5. Thus, theemitter of transistor Q2 is maintained at a fixed voltage, as regulatedby Zener diode D5, despite variations in the power supply connected toinput terminal 24. A junction 36 between the collector of transistor Q1and the timing capacitor C1 is connected to the base of transistor Q2through a decoupling diode D6. A resistor R6 connected from the groundedbuss 30 to the cathode of diode D2 preserves forward potential dropsacross diodes D2 and D3. As will be seen later, the forward potentialdrops across diodes D2 and D3 serve to cancel out the junctionpotentials of diode D6 and the base-emitter of transistor Q2.

The collector of transistor Q2 in the detector circuit 18 is connectedover line 38 to the input of the latch circuit 20. Latch circuit 20, inturn, controls the condition of the output circuit 22 over line 40. Thelatch circuit 20 and the output circuit 22 are preferably constructed inthe manner described in the above-noted Wallentowitz application. Thelatch 20 is triggered from its off state to its "on -state by thedetector 18. When the latch 20 is in its *of state, the output circuit22 is disabled from otherwise Shunting the Operating coil of the outputrelay K1 which is energized by current flow between busses 28, 30 andthrough a current limiting resistor R7. When the latch 20 is triggeredto its "on state by detector circuit 18, the output circuit 22 isenabled to short -out the operating coil with the result that the outputrelay K1 is deenergized-When ouput relay K1 is energized, its normallyopen contacts Kla close to connect the lamp across busses 28, 30.

The output relay K1 includes a second set of relay contacts K117 whichare normally closed when the relay is deenergized so as to short out thetiming capacitor C1 through a current limiting resistor R8. A third setof relay contacts Klc close when the output relay K1 is energized toshort out the switch S1 in order that the switch need only bemomentarily closed in order to initiate an expos-ure time cycle.

Considering the operation of the timer 10, the adjustable tap 31 of thepotentiometer P1 is adjustably preset according to the desiredlumen-second light output of the lamp 12. The voltage tapped from thepotentiometer P1, which is a certain percentage of the fixed potentialdrop developed across Zener diode D4, serves to establish the level ofconduction of transistor Q1. The photosensitive 'resistor R1 varies themagnitude of the charging current conducted through theemitter-collector circuit of transistor Q1 to the timing capacitor C1 inaccordance with the existing light output, in lumens, of the lamp 12.

In order to initiate the timing of an exposure time interval by timer10, the switch S1 is closed to complete the energization circuit for theoperating coil of output relay K1. At this point, the output circuit 22is disabled by the off state of latch circuit 20 so that the Operatingcoil for the output relay K1 is not shunted. The output -relay K1 isenergized, and its relay contacts Kla close to energize lamp 12. Relaycontacts Klc close to electrically by-pass the switch S1, establishing aholding circuit for output relay K1. Consequently, the switch S1 neednot be held down after the holding circuit through relay contacts Klc isestablished. The holding circuit contacts Klc of output relay K1 may beomitted if it is convenient to maintain the switch S1 closed for theentire exposure time interval. Relay contacts Klb open so that thetiming capacitor C1 is no longer shorted on itself.

Timing capacitor C1 now begins to' charge toward the potential acrossthe busses 218, 30. The rate at which timing capacitor C1 charges isdetermined by the level of conductance of transistor Q1 and theresistance of the photosensitive resistor R1. After the expiration of aninterval of time determined 'by the charging rate of capacitor Cl, thepotential at junction 36 falls until it equalsthe potential at junction34. At this point, transistor Q2 in the detector circuit 18 is biased on'with the result that the latch 20 is triggered to its "on state.Latchv20, in turn, conditions the Output circuit 22 so as to short outthe en'ergization circuit for the output relay K1, whereupon (a) saidresistor is adjustable to provide for adjustment of the duration of saidtimed interval.

3. The process timer defined in claim 1 wherein (a) said meansestablishing the current conducting level of `said device is adjustableto provide for adjustment of the duration of said timed interval.

4. A process timer of the class described, comprising,

in combination:

(A) a timing capacitor connectable to be charged from a potentialsource;

(B) a resistor connected in the charging path for said capacitor;

(C) a transistor having (a) an emitter-collector circuit connected inthe charging path for said capacitor, and

l(b) a base;

(D) means connected to the base of said transistor for establishing acurrent conducting level for said emitter-collector circuit;

(E) means establishing a first 'fixed reference potential;

and,

(F) detector means connected to said last named means and saidcapacitor; and,

(a) Operating when said capacitor has charged to a potential having apredetermined relationship to said first fixed reference potential (b)whereby to signal the expiration of a time interval.

5. The timer defined in claim 4 wherein:

(a) said means connected to the base of said transistor includes ('1) aZener diode establishing a second fixed potential; and

(2) a potentiometer connected across said Zener diode for applying anadjustably predetermined fraction of said second fixed potential to thebase of said transistor, and

(b) said means establishing said first fixed reference potentialcomprising a second Zener diode,

(l) said 'first and second Zener diodes having closely matchedcharacteristics.

6. The timer defined in claim 4, and:

(G) a forward biased diode connected in the baseemitter circuit of saidtransistor,

(a) the forward potential drop across said diode being equal andopposite to the base-emitter junction potential of said transistor.

7. The timer defined in claim 6 wherein said detector means comprises:

(a) a second transistor having (1) an emitter connected to said fixedreference potential, and

(2) a base, and

(b) a base circuit diode connecting said base to said tirning capacitor.

8. The timer defined in claim 7 and (H) a pair of forwardly biaseddiodes connected in circuit with said timing lcapacitor and saiddetector means,

(1) the forward potential drop across said pair of diodes being equaland opposite to the sum of the junction potentials of said base circuitdiode and the base-emitter junction of said second transistor in saiddetector.

9. An interval timer of the class described for controlling theoperation of means producing a condition, said timer comprising, incombination:

(A) an electrical potential source;

(B) an interval timing circuit connected to said potential source, saidtiming circuit comprising (a) a capacitor charged from said potentialsource,

(b) a -condition responsive impedance circuit element connected in thecharging path for said capacitor to determine the charging rate thereof;

(1) said element having an impedance value prop'ortional to the level ofsaid condition, and

(c) a detector Operating to signal the expiration of a time intervalwhen said capacitor charges to a predetermined potential; and,

(C) output means responsive to said detector for controlling theoperation of said condition producing means.

10. The timer defined in claim 9 wherein said interval timing circuitfurther comprises:

(d) adjustably preset means connected in the charging path for saidcapacitor to establish a desired time integra'ted condition output,

V(l) said connection producing means being controlled such that thecondition output over the interval timer is equal to said desiredcondition output.

11. The timer defined in claim 10 wherein said adjustably preset meanscomprises:

(2) a transistor having an emitter-collector circuit connected in saidcharging path, and

(3) means deriving an adjustably preset potential for application to thebase of said transistor tov control the conductance of saidemitter-collector circuit.

12. An interval timer of the class described for providing a selectablypredetermined lumen-second output of a lamp irrespective of lampdete'rioration and fluctuations in lamp supply voltage, said timercomprising, in combination:

(A) a capacitor connectable to be charged from a potential source;

(B) a photosensitive resistor connected in the charge path for saidcapacitor,

(a) said photosensitive resistor being optically coupled to said lamp,and

(b) having a resistance value Proportional to the level of light outputfrom said lamp;

(C) a Varia-ble current conducting device connected in the charge pathfor said capacitor,

(a) said device having a control input;

(D) means connected to the control input of said device for establishinga level of current conduction;

(E) means establishing a fixed reference potential;

(F) detector means connected to said last named means and saidcapacitor,

(a) said detector operating when said capacitor has charged to apotential having a predetermined realtionship to said fiXed referencepotential to signal the expiration of a timed interval measured fromwhen said capacitor was connected to said potential source; and,

(G) output circuit means connected to said detector and said potentialsource, said output circuit means (a) Operating to ena'ble theenergization of a lamp upon connection of said capacitor to said voltagesource, and

(b) Operating in response to said detector upon the expiration of saidtimed interval to disable the ene'rgzation of the lamp.

13. The timer defined in claim 12 wherein 'said output circuit meanscomprises:

(a) an output relay having relay contacts Operating in the energizationvcircuit for the lamp, and

(b) a -bistable latch circuit having (1) a first stable state effectiveto enable the energization of said output relay to close said relaycontacts, and

(2) a second stable state to which said latch is triggered by saiddetector effective to disable the energization of said output relay,

(3) said latch automatically reverting to its first stable state upondisconnection of said output circuit means from said voltage source.

14. The timer defined in claim 12 wherein:

the output relay is de-energized. Relay contacts Kla open to de-energizethe lamp 12. At the same time, relay contacts Klb close to dischargecapacitor C1, and relay contacts Klc open to disconnect the positivebuss 28 from the power input terminal 24. The moment of de-energizationof the output relay K1 signifies the expiration of the exposure timeinter'val during which the desired lumensecond quantity 'of light hasbeen given off by the lamp 12 as determined by the setting of thepotentiometer P1. With the removal of power, the latch circuitautomatically reverts to its o state in which it remains until againtriggered by detector circuit 1'8. When capacitor C1 is fully dischargedthrough relay contacts Klb, the switch S1 may be closed to initiate thetiming of another exposure time interval.

The adjustab'ility of the timer afforded by the selecti've setting ofthe potentio'meter P1 for different exposures in a photocopying process,as Well as the compensation of the controller for power sourcefluctuations and lamp deterioration, can perhaps best be demonstrated bythe following mathematical analysis of the circuit operation. Thecharging current Ic 'for ti-ming capacitor C1 is constant when underconditions of equilibrium:

k=setting of potentiometer P1;

VD1=fixed potential drop across Zener diode D4; VQ1=base-emitterjunction potential of transistor Q1; VD1=for'ward potential drop acrossdiode D1; R1=resistance of photosensitive resistor R1.

By selecting diode D1 such that its junction potential matches that ofthe base-emitter junction of transistor Q1, the terms VQ1 and V131cancel from the above equation. Therefore:

Since, at equilibrium, the charging current Ic is constant, thepotential V01 across the timing capacitor C1 as a function of time t canbe expressed as:

where C1=capacitance of capacitor C1 in farads. Substituting for Ic inthe above equation:

Inasmuch as diodes D2 and D3 are selected for their ability to cancelout the junction potentials of diode D6 and the base-emitter junction oftransistor Q2, this transistor will conduct to signal the expiration ofan exposure time interval when VC1=VD5 (the fixed voltage drop acrossZener diode D5). Consequently the time tc of an exposure time interval'may be expressed as:

It will be observed that if Zener diodes D4 and D5 are fairly closelymatched both as to potential drop and temperature coefficients, theexposure time tc is compensated for temperature variati-ons as far asthe terms V114 and V135 are concerned. The effects of temperature on theterms R1 and C1 can be compensated for by making the temperaturecoefiicients of the photosensitive resistor R1 and timing capacitor C1equal and opposite.

It will further be observed that the a'bove expression for tc is ageneral expression for an interval timer and is not necessarily limitedto an exposure ti-me (lumen-second) controller. 'I'he time interval isseen to 'be directly proportional to the resistance value R1 andinversely proportional to the setting k of the potentiometer P1.Moreover, since the supply voltage does not enter into the expression,the time interval is independent of supply voltage fluctuations.

Considering the disclosed application where the photo- Sensitiveresistor R1 response to the existing light level output of lamp 12, itsresistance R1 may be expressed as:

where \=light le'vel of lamp 12 is lumens; and m=constant ofproportionality. Substituting for R1 in the above equation for theexposure time interval and arranging terms, we obtain:

It will thus be observed that the term Nie represents lumen-secondswhich is solely determined by the adjusted setting k of potentiometerP1; all other terms being constants. The timer 10 automatically adjuststhe exposure time so as to compensate for variati'ons in the lightoutput of lamp 12 caused by power source fluctuations and lampdeterioration. Consequently, the lumen-second light output of lamp 12 isheld constant for a particular setting of potentio'meter Pl in spite ofvariations in the light output level.

Although the invention has been disclosed in its specific application asa lumen-second controller, it 'will be observed from the aboveexpression tc: VD5R1C1/kVD1 that it has applicability as a conditionresponsi-ve timer in a Wide variety of control applications. Theinterval timer is readily made variable 'by adjustment of the setting kof potentio'meter P1 or by adjustment of a manually variable resistorsubstituted for photoresistor R1. In addition, the timer can be readilycompensated for temperature and is inherently insensitive to powersupply variations.

It will be appreciated that the resistance R1 may be constituted by someother form of element responsive to a condition other than light, andthe controller implemented to control means producing that particularcondition. Thus, the time integrated control function performed by thetimer, as in the disclosed application, is rendered independent ofspurious variations in the condition level.

It will thus be seen that the objects set forth abo've, among those madeapparent from the preceding description, are efliciently attained and,since certain changes may be made in the above construction withoutdeparting from the scope of the invention, it is intended that allmatter contained in the above description or shown in the accompanyingdra-Wing shall be interpreted as illustrative and not in a limitingsense.

It is also to be understood that the following claims are intended tocover all of the generic and specific features of the invention which,as a matter of language, might be said to fall therebetween.

Having described my invention, 'what I claim as new and desire to secureby Letters Patent is:

1. A condition responsive process timer comprising, in combination:

(A) A timing capacitor connectable to be charged from a potentialsource;

(B) A constant current source connected in the charging path for saidtiming capacitor, including;

(a) a resistor connected in the charging path for said capacitor,

(b) a variable current lconducting device connected in the charging pathfor said capacitor in series with said resistor, and

(c) means connected to said variable conductance device for establishingthe current conducting level thereof;

(C) A detector connected in circuit with said last named means and saidtiming capacitor;

(a) said detector Operating when said capacitor has charged to apredetermined potential relative to said fixed reference potential tosignal the expiration of a timed interval.

2. The process timer defined in claim 1 wherein (a) said variableconducting device is a transistor having (1) an emitter-collectorcircuit connected in said charging path, and

(2) said control input is the base of said transistor.

15. The timer defined in claim 14 Wherein (a) said means connected tothe base of said transistor includes (l) a Zener diode establishing afixed potential,

and

(2) a potentiomete'r connected across said Zener diode for applying anadjustably predetermined fraction of said fixed voltage to the base ofsaid transistor, and

(b) said means esta'blishing said fixed reference potentian comprising asecond Zener diode,

(1) said first and second Zener diodes having closely matchedcharacteristics.

16. The timer defined in claim 15 further comprising: (H) a forwardbia'sed diode connected in the baseemitter circuit of said transistor,

(a) the forward potential drop across said diode being equal andopposite to the base-emitter junction potential of said transistor.

17. The timer defined in clam 16 wherein said detector means comprises:

(a) a second transistor having (1) an emitter connected to said meansproducing a fixed reference potential, and

(2) a base, and

(b) a diode connecting said base to said timing capacitor.

18. The timer defined in clam 17 further comprises:

(I) a pair of forwardly biased diodes connected in crcuit with saidti'ming capacitor and said detector means,

(1) the forward potential drop across said pair of diodes being equaland opposite to the sum of the junction potentials of said diode 'andthe base-emitter junction of said second transistor in said detectormeans.

References Cited UNITED STATES PATENTS 3,205,799 9/1965 Burgarella etal. 95-10 3,324,779 6/1967 Nobusawa et al 88 24 X 3,326,103 6/1967 Topaz95- 10 NORTON ANSHER, Primary Examner.

25 RICHARD A. WINTERCORN, Assistant Examiner.

